The invention relates to an apparatus and method for retarding vehicles powered by internal combustion engines, typically diesel engines, by releasing compressed gases from each cylinder through its exhaust valve during a compression stroke and near the top dead centre position and during the same time opening the exhaust valve of a cylinder on an intake stroke.
Truckers commonly encounter the problem of slowing heavy trucks, usually diesel powered trucks, on long down-grades. It is well known that excessive use of conventional brakes leads to premature brake wear and to overheating of the brakes. Consequently it is well known to fit diesel engines with compression release retarding devices which slow the trucks due to the action of the compression of their engines. It is commonly assumed that the high compression of a diesel engine yields significant braking effect when the accelerator is released, and the fuel supply thereby reduced, while coasting down hill. However, one must consider the rebound effect of the compressed gases in each cylinder following the compression stroke and prior to the expansion stroke. The compression stroke may be likened to a spring, each piston acting against the spring to slow the vehicle on its compression stroke. However, the compressed "spring" stores energy which acts against the piston to accelerate the vehicle on the expansion stroke even though the fuel supply has been cut. The previously known retarding devices crack open the exhaust valve of each cylinder during the compression stroke and near the top dead centre position. The compressed gases are thereby discharged through the exhaust system of the engine and have no rebound effect on the piston.
Conventionally, for engines having a push rod or push tube actuated fuel injector, the force to crack open each exhaust valve may be provided by a slave hydraulic piston coupled in a closed hydraulic circuit with a master hydraulic piston actuated by the push rod or push tube for the fuel injector. One problem, however, was to provide a suitably timed pulse of high pressure hydraulic fluid to depress the exhaust valves for engines not equipped with fuel injector push rods or push tubes. Various arrangements have been suggested which involve complicated hydraulic plumbing in some cases.
Patents have been issued for related devices including the following United States patents assigned to Jacobs Manufacturing Company: U.S. Pat. Nos. 4,592,319; 4,399,787; 4,398,510; 4,473,047; 4,423,712; 4,395,884; 4,474,006; 4,485,780; 4,510,900 and 4,572,114.
However, even in view of these prior art devices, the need exists for a relatively simple and reliable retarding device capable of operation on engines without fuel injector push rods and which, at the same time, offers improved performance over conventional units.